The present invention relates generally to a method for making a key for a lock. More particularly, the present invention relates to a method for making keys for a motor vehicle ignition system that is secured by an electronic interlock.
Various types of vehicle security systems have evolved as a way to inhibit, or at least deter, theft of automobiles. One such security system employs an ignition key having an embedded resistor pellet. The resistor pellet, as the name implies, incorporates an electrical resistor of known value. When the key is inserted into the automobile ignition slot and turned, electrical current flows through the resistor. Electronics within the ignition system measure the resistance value of the resistor contained in the resistor pellet and compare the measured resistance value to an expected resistance value. If the measured resistance value falls outside an acceptable resistance range, the vehicle engine cannot be started.
Manufacturing vehicle ignition keys with resistor pellets has proven to be challenging. Manufacturing techniques employed to date include use of adhesives, sonic welding, and swaging. However, the application of each of these techniques has proven problematic for various reasons.
Therefore, there is a need for a method of manufacturing keys with resistor pellets which overcomes problems associated with prior art assembly methods.
The present invention eliminates the difficulties and disadvantages of the prior art by providing a method for assembling an anti-theft key. In a preferred embodiment, the method includes providing a key blade defined by a shank portion (for being inserted into a vehicle ignition) and a handle portion. A through opening is formed in the shank portion of the key blade. A resistor pellet is also provided, the resistor pellet being configured to include an electrically insulative body having a first end including a flange with a perimeter larger than the perimeter of the through opening in the shank portion of the key blade. A second end of the insulative body has a perimeter smaller than the perimeter of the through opening. A resistor contained in the insulative body includes two electrical contact points with electrical conductors connected to each of the contact points and extending beyond the two ends of the insulative body. The second end of the resistor pellet insulative body is inserted through the through opening of the key blade shank portion such that the resistor pellet is loosely positioned within the through opening. With the resistor pellet in position, a second flange having a perimeter larger than the through opening of the key blade shank portion is attached to the second end of the insulative body, thereby capturing the resistor pellet within the through opening by the two flanges positioned on either side of the key blade.
Various methods for attaching the second flange to the second end of the insulative body may be employed in the practice of the invention. In a preferred embodiment, the second flange is formed in place by a polymeric molding process. The polymeric molding process may be implemented in various ways with injection molding being a particularly preferred method for thermoforming the second flange in place. If desired, the polymeric molding process employed to form the second flange may also be employed to form a handle adjacent the handle portion of the key blade substantially simultaneously with the forming of the second flange.
The above described resistor pellet may be further configured to include a lip adjacent the second end of the insulative body and extending beyond an outer surface of the key blade shank portion when the second end of the insulative body is fully inserted through the through opening. When the resistor pellet is configured in this manner, a gap is formed between the lip and the through opening. Polymeric material can then be injected into the gap during the polymeric molding process to provide superior attachment of the second flange once the material has hardened.